1. Field of the Invention
The invention is in the field of transporting workpieces into and out of sealable chambers which are evacuated or maintained under some other extreme environment.
2. Description of the Prior Art
In order to obtain optimum production with most vacuum processing apparatus, particularly vacuum coating apparatus, the desired process pressure is maintained continuously in the chamber containing the coating or other process equipment. Workpieces enter and leave via an adjacent chamber, conventionally called a vacuum lock, which can be selectively opened to or isolated from the process chamber by a gate valve. Such an apparatus is described in U.S. Pat. No. 3,641,973 to Shrader. In some devices, such as that described in U.S. Pat. No. 3,656,454 to Shrader, the workpieces entered via one lock and left via a second lock. In both of these prior systems, a relatively large lock was required because the lock had to contain a large holder which could simultaneously expose twenty or more substrates to the coating equipment.
In the workpiece handling system of U.S. Pat. No. 3,584,847 to Hammond, Jr. et al, substrates were removed from a cassette in an entrance lock and placed horizontally onto a linear conveyor for processing. Processed substrates were placed in another cassette for removal from an exit lock. In the system of U.S. Pat. No. 4,047,624 to Dorenbos, a number of workpieces were placed in a cassette-like carrier which was placed on the open door of a vacuum lock. When the door was closed, the carrier was swung into the lock and was then conveyed through a gate valve into a holding chamber. The wafers were unloaded from the carrier and placed vertically onto a linear conveyor for processing. The processed wafers were loaded into another carrier and removed through an exit lock similar to the entrance lock.
Recently, cassette-to-cassette vacuum processing systems for semiconductor wafers have become commercially available. In some of these systems, wafers are removed from a cassette in a cassette elevator and placed onto a belt conveyor. The wafers are transferred through a vacuum lock onto a horizontal rotating table in a processing chamber by means of a rotary transfer arm. Processed wafers are removed through the same lock onto a second conveyor which deposits them in a cassette in a second cassette elevator. U.S. Pat. No. 4,311,427 to Coad et al describes a system for transferring wafers one at a time through a vacuum lock into (or out of) a cassette.
Several moving floor conveyors, including a so-called walking beam conveyor, are described in U.S. Pat. No. 4,275,978 to Brooks et al. In these conveyors, workpieces are supported on a horizontal array of slats. Several of the slats are rotated up out of the plane of the remainder so that an object placed on the array is lifted and advanced incremently along the array.